Laboratory Methods of Organic Chemistry - Sciencemadness Dot Org

398 CONSTITUTION OF BIOSBS
HC ^ 0 CH,OH
Lactose
According to Haworth cellobiose differs from maltose only in having
the j8-glucosidal configuration. Lactose and cellobiose are built up in
identical fashion and differ only in their monose components. Gentiobiose
is a ^-biose ; the common oxygen bridge, however, is attached at
C6. The formulae show at the same time the configurations of the constituent
monoses.
The fundamental principles governing the spatial isomerism of the
simple sugars and the theoretical and experimental work of Emil Fischer
cannot be dealt with here. Those who are not already familiar with
the subject should at once fill this gap in their knowledge; they are
emphatically advised to use space models.
Those bioses in which the aldehydic (cyclo-acetal) carbonyl group is
free have a reducing action (on Fehling's solution).
Experiment.-—Boil samples of both sucrose and lactose with
Fehling's solution.
See p. 298 for information about the production of the osazones of
the simple sugars. The osazones of rf-glucose, rf-fructose, and rf-mannose
are identical.
The number of synthetic bioses is increasing ; among natural bioses
gentiobiose (see above) has been obtained synthetically from d-glucose
by the action of emulsin (Bourquelot). Attempts at synthesis with the
bromoacetyl-sugars do not succeed because the desired OH-group of the
second molecule is not attacked. The bromoacetyl-sugars are formed,
quite generally, by the action of acetyl bromide on the sugars.
The synthesis of lactose has been described very recently by A.
Pictet. Helferich has also been successful in synthetic work of this
kind.
Of other recent experiments in the chemistry of the sugars the preparation
of the anhydro-sugar laevoglucosan C6H10O8 by the rapid distillation
of starch or cellulose in a vacuum may be mentioned (Pictet).
This interesting compound possibly has the constitution I.